Most motor vehicles have powerplants in which fuel is combusted to generate heat for operating the powerplant. Typical powerplants are internal combustion engines, either spark-ignition (gasoline) or compression-ignition (diesel). A running engine also operates various accessory devices like an alternator, air conditioner compressor, power steering pump, etc.
An alternator generates electricity that supplies the needs of the vehicle electrical system including maintaining state-of-charge of a battery bank that comprises one or more D.C. storage batteries.
Diagnostic testing of the various portions of the electrical system, such as the charging system, may be performed on occasion to assure that they are operating properly and/or to diagnose possible faults in the system, including faulty devices, faulty wiring, and faulty connections. Various diagnostic test devices are commercially available. One such device bears the name “InTELLECT EXPHD”.
The “InTELLECT EXPHD” comprises a handheld unit and various test cables for connecting the handheld unit to various portions of an electrical system to enable a technician to perform various diagnostic tests. The handheld unit comprises an expandable electronic platform for performing various diagnostic test algorithms, including battery/alternator testing.
For performing a diagnostic test and acquiring test result data, the device comprises a keyboard, a display, and various ports and interfaces. The ports provide for connection of various test cables to the handheld unit. The interfaces provide for data transmission to other devices, such as transmission of a test report to a printer.
When the “InTELLECT EXPHD” is used to test the battery charging system, one end of an electrical cable that is sometimes called an AMP CLAMP is connected to a mating port of the handheld unit. At the opposite end, the AMP CLAMP comprises an electrical coil that can be clamped around the exterior of one or more wires or cables so that electric current flowing through the wires/cables passes through the interior of the coil. The current creates magnetic flux that passes through the interior of the coil, with the magnitude of the magnetic flux being correlated with the magnitude of the electric current.
A typical charging circuit diagnostic test procedure comprises placing the AMP CLAMP around one or more cables that connect the alternator positive output terminal to the positive terminal of the battery bank and then selectively turning various electrical devices in the vehicle on and off to selectively load and unload the electrical system. The effect of connecting and disconnecting various devices is detected via the AMP CLAMP, with changes in flux caused by changes in current providing data input to the handheld unit. The collected data is then analyzed and evaluated. Battery voltage and alternator voltage are also monitored during the test for analysis in conjunction with current measurements.
The inventor has observed that the use of existing electrical devices in a motor vehicle to load the vehicle's electrical system for the purpose of evaluating the charging system may not assure the best accuracy of such an evaluation. Switching various devices on and off may not provide a range of loading that will enable the full load rating of the alternator to be tested because the alternator, if properly rated for the expected loads that may be imposed on it, is unlikely to be loaded to the full extent of its rating simply by turning various loads in the vehicle on and off.
For performing certain tests such as the battery charging test, it is known to connect a load bank directly across the alternator output. Depending on the particular type of test equipment being used, electrical sensors, such as the AMP CLAMP and/or one or more voltmeters, are used to measure current/voltage parameters of interest during the test. The test typically involves running the engine at different speeds and setting the load bank to different load settings.
Because the battery bank and the alternator are located at various locations in the vehicle that are remote from the occupant compartment, the load bank is also remote from the occupant compartment when connected across either the battery bank or the alternator. Yet many of the various tasks associated with the diagnostic test procedure, such as accelerating the engine, need to be performed from the occupant compartment.
When a diagnostic test procedure requires that the load that is imposed by the load bank on the electrical system be changed at various times during the test, either a test technician who is in the vehicle must get out, change the load, and re-enter the vehicle, or else a second technician must be present to change the load while the first technician remains in the vehicle.
A load bank can be connected to a point in certain electrical circuits in a motor vehicle that is fed from the battery bank through a cable or cables in order to test the integrity of the cable or cables and their connections without the circuit load drawing any current. One example would be testing the feed to the cranking motor of a large diesel truck which has a mag switch. A load bank can also be used to test the feeds to other circuits if the circuit loads are temporarily disconnected from the feeds so as not to interfere with the load bank. The ability to remotely operate the load bank when any vehicle circuit is being tested is a significant advantage in terms of test time, test convenience, and efficient use of test technician personnel.